The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems are used to deposit or remove films on a substrate. During processing, a photoresist layer may be deposited on the substrate. The photoresist layer may then be patterned to define masked and unmasked regions for subsequent ion implantation. During the ion implantation, ions of a material are accelerated in an electrical field and directed at the substrate. The ions are used to change physical, chemical, and/or electrical properties of the substrate. The masked regions of the substrate are used to block the ions. The ions are implanted in an exposed layer of the substrate in the unmasked regions. When the ion implantation steps are complete, the photoresist mask is usually removed before additional processing is performed.
Referring now to FIGS. 1A to 1C, methods for processing a substrate are shown. In FIG. 1A at 20, a photoresist layer is formed on an outer surface of a substrate, for example using spin coating or other suitable methods. At 22, the photoresist layer is patterned into masked and unmasked regions. At 24, the substrate is bombarded with ions. The ions are implanted into the substrate in the unmasked regions of the substrate. The photoresist layer in the masked regions of the substrate blocks the ions. During subsequent processing, the photoresist layer is removed at 26. At 28, further processing of the substrate is performed.
In FIG. 1B, the photoresist layer may be exposed to ultraviolet (UV) light at 30 to cross-link the photoresist. Exposure to the UV light is performed prior to bombardment with ions at 24.
In FIG. 1C, a method for removing the photoresist layer after ion bombardment is shown. At 34, the substrate is arranged in a processing station. At 36, the substrate is heated to a predetermined temperature. In some examples, the substrate is heated to a temperature of 285° C. At 38, process gases are supplied to the processing station, plasma is supplied or struck, and the plasma strips the photoresist.
High ion implant doses (greater than about 1×1015 ions/cm2) into the masked regions of the photoresist layer may generate a hard carbonaceous crust layer on an outermost surface of the photoresist layer. In some examples, the crust layer has a thickness of approximately 700 Angstroms. In addition, the ion implantation process breaks down the underlying photoresist into smaller and more volatile fractions by a chain scission mechanism and by a photoresist deprotection reaction caused by photoacid being generated by the ion implantation process.
Removal of the crust layer using plasma requires elevated temperatures due to a high activation energy of the crust layer/plasma reaction (1.6-2.6 eV). However, the implanted photoresist has a propensity to explode or pop when heated due to gas pressure being released by fractionated photoresist under the crust layer. The popping creates defects and causes line breaks. Some methods reduce the strip process temperature below a temperature at which popping occurs. However, these lower temperatures also significantly reduce the ash rate and throughput.
As shown in FIG. 1B, exposing the substrate to ultraviolet (UV) light has been used prior to ion implantation to crosslink the photoresist layer. This approach makes the substrate less prone to popping but the UV exposure causes critical dimension (CD) loss. Additionally with the advent of chemically amplified photoresists, the UV exposure also generates photoacids, which when heated cause the deprotection reaction and generate the unwanted volatile compounds the UV exposure was designed to inhibit.